Does a 250w MH DE bulb actually produce 500w of light?...

[Stlouisguy]

Or is it just somewhere above 250w+

Right now I have 3 250w 10k DE MH and 2 150w 20k DE MH above my tank. Im trying to figure out how much light I am pushing to the floor of the tank (tank is 30 inches deep converted Oceanic 175 bowfront). Im hoping its closet to the 2100 watts of light and not the 1000 watts of light. Any lighting experts out there?

On a side note, its almost time for a bulb change (coming up on a year) and wondering if it would hurt to switch the 10k for 20 k and visa versa to get a bit more blue in the tank.

Thanks all!

 

[clayswim]

250W bulbs have a hard time reaching that far into water, and very little of the 150W will penetrate that deep. If you want to place something like clams, anemones or light-loving corals on or near the bottom you might want to consider switching to 400W. How much blue you use is completely up to you. Many corals prefer a little more red-yellow for growth, but blue penetrates better through the water; meaning a greater percentage of the 20K will reach the depths of the tank.

As for the question "Does a 250w MH DE bulb actually produce 500w of light?..." It's a hard question to answer because it depends on what you're comparing it to; and even then it's rather impossible to answer. Fluorescent lights simply don't penetrate into water that far, no matter how many tubes you place over the tank. This is because of their lack of intensity. Incandescent, halogen, mercury vapor and high and low pressure sodium bulbs are out of the question due to their lack of proper spectrum. So what we're left with for a tank that deep is metal halide. 150W/175W bulbs are fine up to about 18-22", 250W bulbs start to get weak around 24" or slightly more, and 400W are good to about 36". Anymore than that and you have to fork out the money for the 1000W systems. Even these general rules have their quirks. For instance, the 175W will actually reach the bottom of deep tanks, but only directly beneath the bulb. The larger wattages will spread out farther, covering more area on the bottom with bright light. That's the reason fluorescent tubes work great in shallow tanks; their coverage is evenly spread.

Clayton

 

[Stlouisguy]

Thanks for the info. I remeasured the tank and its 29 1/2 inches. I have about a 2" sandbed to 27ish deep. I have a clam on the bottom and its about doubled in size. I havent tried sps on the bottom yet because I was worried about the depth.

Can I go to 400 watt bulbs when it came with 250? Does the Ballast handle differant bulbs like that because I cant change that part of the lighting (too costly). I dont mind going up to 3x 400 DE and 2x 250 DE if it would greatly benefit the tank and my coral

 

[clayswim]

400W bulbs can't be used on 250W ballasts, so you would have to replace the ballast too. It depends on the clam, but some species are about as sensitive to light as SPS corals are. If your clam is doing fine I don't think I'd worry about it too much. If you're concerned about weak lighting with SPS just place them a little higher in the tank and directly under a bulb. 1/4 of the way up your tank from the top of the sand bed is about 20", which should be shallow enough for any of your lights.

Clayton

 

[bc_slc]

After briefly skimming through your post, I missed what type of reflector you are using. There is a pretty big difference in the DE market. If it is a reef optix III or a PFO mini, then you are fine with 250watts x3 over the tank. My tank is 30" Tall and that is what I run. Don't worry about upgrading.